Thin film photovoltaic cell with back contacts

ABSTRACT

Photovoltaic cells, photovoltaic devices, and methods of fabrication are provided. The photovoltaic cells include a transparent substrate to allow light to enter the photovoltaic cell through the substrate, and a light absorption layer associated with the substrate. The light absorption layer has opposite first and second surfaces, with the first surface being closer to the transparent substrate than the second surface. A passivation layer is disposed over the second surface of the light absorption layer, and a plurality of first discrete contacts and a plurality of second discrete contacts are provided within the passivation layer to facilitate electrical coupling to the light absorption layer. A first electrode and a second electrode are disposed over the passivation layer to contact the plurality of first discrete contacts and the plurality of second discrete contacts, respectively. The first and second electrodes include a photon-reflective material.

BACKGROUND

A thin film solar cell (TFSC) or thin film photovoltaic cell (TFPV) is asecond generation solar cell made by depositing one or more thin layers,or thin films (TFs), of light absorption material on a substrate, suchas a glass, plastic or metal substrate. Thin film solar cells arecommercially used in several technologies, including cadmium telluride(CdTe), copper-indium-gallium-selenide (CIGS), and amorphous and otherthin film silicon (a-Si, TF-Si). There are other second generation thinfilm photovoltaic cell technologies that are in early stage of research.These include copper-zinc-tin-sulfide (CZTS) and Perovskite solar cells.

Film thicknesses can vary from a few nanometers to tens of micrometers,much thinner than the conventional, first generation crystalline siliconsolar cell (c-Si), which typically utilize silicon wafers of, forinstance, 200 micrometers thickness or greater. This differenceadvantageously allows thin film photovoltaic cells to be flexible, lowerin weight, and have less drag compared with first generation solarcells.

In order for thin film photovoltaic cell technology to make furtheradvances in the marketplace, improved thin film photovoltaic celldesigns are desired, with reduced recombination losses and reducedcontact resistances. There is also a need for reduced absorber materialthicknesses to increase manufacturing throughput of the thin filmphotovoltaic cell, such as with, for instance, CIGS, CZTS, Perovskite,etc., solar cells.

BRIEF SUMMARY

The shortcomings of the prior art are overcome and additional advantagesare provided through the provision of a photovoltaic cell, whichincludes, for instance: a substrate, the substrate being, at least inpart, transparent to allow light to enter the photovoltaic cell throughthe substrate; a light absorption layer associated with the substrate,the light absorption layer having opposite first and second surfaces,the first surface being closer to the substrate than the second surface;a passivation layer disposed over the second surface of the lightabsorption layer; a plurality of first discrete contacts and a pluralityof second discrete contacts, the plurality of first discrete contactsand the plurality of second discrete contacts both residing, at least inpart, within the passivation layer, and facilitating electrical couplingto the light absorption layer; and a first electrode and a secondelectrode disposed over the passivation layer and comprising a photonreflective material, the first electrode contacting the plurality offirst discrete contacts and the second electrode contacting theplurality of second discrete contacts.

In another aspect, a photovoltaic device is provided which includes aphotovoltaic cell. The photovoltaic cell includes, for instance: asubstrate, the substrate being, at least in part, transparent to allowlight to enter the photovoltaic cell through the substrate; a lightabsorption layer associated with the substrate, the light absorptionlayer having opposite first and second surfaces, the first surface beingcloser to the substrate than the second surface; a first surfacepassivation layer and a second surface passivation layer, the firstsurface passivation layer being disposed over the first surface of thelight absorption layer, between the substrate and the light absorptionlayer, and the second surface passivation layer being disposed over thesecond surface of the light absorption layer; a plurality of firstdiscrete contacts and a plurality of second discrete contacts, theplurality of first discrete contacts and the plurality of seconddiscrete contacts both residing, at least in part, within the secondsurface passivation layer, and facilitating electrical coupling to thelight absorption layer; and a first electrode and a second electrodedisposed over the second surface passivation layer and comprising aphoton-reflective material, the first electrode contacting the pluralityof first discrete contacts, and the second electrode contacting theplurality of second discrete contacts.

In a further aspect, a method is presented which includes fabricating aphotovoltaic cell. The fabricating includes: providing a substrate, thesubstrate being, at least in part, transparent to allow light to enterthe photovoltaic cell through the substrate; providing a lightabsorption layer in association with the substrate, the light absorptionlayer having opposite first and second surfaces, the first surface beingcloser to the substrate than the second surface; disposing a passivationlayer over the second surface of the light absorption layer; forming aplurality of first discrete contacts and a plurality of second discretecontacts within, at least in part, the passivation layer to electricallycouple to the light absorption layer; and providing a first electrodeand a second electrode disposed over the passivation layer andcomprising a photon-reflective material, the first electrodeelectrically contacting the plurality of first discrete contacts, andthe second electrode electrically contacting the plurality of seconddiscrete contacts.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a process of fabricating a photovoltaiccell, in accordance with one or more aspects of the present invention;

FIGS. 2A-2I depict one detailed embodiment of an exemplary photovoltaiccell being fabricated, in accordance with one or more aspects of thepresent invention; and

FIG. 3 depicts a plan view of one embodiment of the first and secondelectrodes of the photovoltaic cell of FIG. 2I, in accordance with oneor more aspects of the present invention.

DETAILED DESCRIPTION

Aspects of the present invention and certain features, advantages, anddetails thereof, are explained more fully below with reference to thenon-limiting examples illustrated in the accompanying drawings.Descriptions of well-known materials, fabrication tools, processingtechniques, etc., are omitted so as not to unnecessarily obscure theinvention in detail. It should be understood, however, that the detaileddescription and the specific examples, while indicating aspects of theinvention, are given by way of illustration only, and not by way oflimitation. Various substitutions, modifications, additions, and/orarrangements, within the spirit and/or scope of the underlying inventiveconcepts will be apparent to those skilled in the art from thisdisclosure.

As understood in the art, photovoltaics generally refers to convertingsolar energy into direct current electricity using semiconductormaterials that exhibit the photovoltaic effect. A photovoltaic systememploys solar panels comprising a number of photovoltaic cells to supplyusable solar power. Current second generation solar or photovoltaiccells employ thin film semiconductor materials as the solar absorber orlight absorption layer. A number of semiconductor materials have beenproposed or used in thin film solar cells, includingcopper-indium-gallium-selenide (CIGS), copper-zinc-tin-sulfide/selenide(CZTS), and organic- or inorganic-Perovskite, along with others.Conventional thin film photovoltaic cells include an absorber materialdisposed between an ohmic contact and a transparent contact, whichallows light to reach the absorber layer.

One way to reduce cost of energy for photovoltaic cell systems is toimprove efficiency of the device. Proper identification and eliminationof loss mechanisms, while optimizing the cost of the manufacturing ofthe device, can lead to further cost reduction and aid in scaling of thelevelized cost of electricity (LCOE) of the technology, while the solarindustry is ramping up manufacturing capacity into the multi-GW-scale.One large contribution to losses is recombination at the front andback-side surfaces of the light absorber to the front and back contacts,respectively. A need therefore continues to exist for improved thin filmsolar cell designs with reduced recombination losses, and for thinabsorbers with reduced contact resistance. In addition, there is a needto reduce absorber thickness to increase manufacturing throughput inthin film solar cell manufacturing of certain photovoltaic cells, suchas CIGS/CZTS cells.

Typically, for thin film solar cells, the back-side contact as well asthe front-side contact are continuous, stratified media. Transparentconducting oxides, used as a front surface cell contact, and windowlayers, such as CdS are often responsible for ohmic losses and opticallosses. Also, monolithic integration of absorber segments leads tolosses at segmentation scribes.

Presented herein are thin film photovoltaic cells with both contacts (ortypes of contacts) to the light absorption layer on the same side of theabsorber. This advantageously allows separate optimization of theoptical design, and electrical design. The configurations disclosedherein remove the requirement for a transparent conducting oxide (TCO)layer, and allow for improved passivation of the light absorptionsurfaces, while also allowing for simplified electrical interconnectionof the cells. This is achieved, in part, by structuring nano-sizeddiscrete contacts or vias into and through a common passivation layer onone side of the absorber to provide both ohmic, as well as rectifying,contacts to the absorber material. In other embodiments, the differentcontacts may be charge-carrier selective contacts. Advantageously,disclosed herein are thin film solar devices, such as CIGS, CZTS,Perovskite cells, etc., with an all back-side contact approach usingnano-sized point contacts. Note that “front-side” in this context refersto the side light enters through, while “back-side” refers to theopposite side.

The back-side-only photovoltaic cells and manufacturing methodsdisclosed address numerous goals, including, for instance, reducing thethickness of the thin film light absorption layer (i.e., the thin filmsolar absorber), reducing surface recombination, and increasingphotovoltaic cell efficiency.

Generally stated, disclosed herein are photovoltaic cells (and methodsof fabrication thereof) which include: a substrate, and a lightabsorption layer which comprises, for instance, a thin film lightabsorption semiconductor material. The substrate is transparent to allowlight (such as visible light) to enter the photovoltaic cell through thesubstrate, and the semiconductor material may have a thickness of 5microns or less, for instance, the material may have a thickness in therange of 0.5-2 microns. The light absorption layer has opposite firstand second surfaces, with the first surface being closer to thesubstrate than the second surface. A passivation layer is disposed overthe second surface of the light absorption layer, and a plurality offirst discrete contacts and a plurality of second discrete contacts areprovided within the passivation layer, arrayed in any desiredconfiguration. The first and second discrete contacts are different setsof different types of sub-micrometer point contacts, which aredistributed within the thin passivation layer and which facilitateelectrical connection to the light absorption layer, as explainedfurther herein. In addition, a first electrode and a second electrodeare provided over the passivation layer to electrically contact theplurality of first discrete contacts and the plurality of seconddiscrete contacts, respectively. The first and second electrodes mayadvantageously comprise a photon-reflective material, which forms thebackside of the photovoltaic cell.

In certain embodiments, the semiconductor material of the lightabsorption layer may comprise a second or later-generation material,such as copper-indium-gallium-selenide (CIGS),copper-zinc-tin-sulfide/selenide (CZTS), organic- orinorganic-Perovskite, by way of example only.

In one or more implementations, the passivation layer is a secondsurface passivation layer (which resides over the second surface of thelight absorption layer), and the photovoltaic cell may also include afirst surface passivation layer disposed over the first surface of thelight absorption layer, between the substrate and the light absorptionlayer. By way of example, the first surface passivation layer and thesecond surface passivation layer may comprise a common passivationmaterial, such as aluminum oxide, as one example.

In certain implementations, the plurality of first discrete contacts maycomprise a plurality of heterojunction-type discrete contacts (or vias)to the light absorption layer, and the plurality of second discretecontacts may comprise a plurality of ohmic-type discrete contacts (orvias) to the light absorption layer. For instance, the light absorptionlayer may comprise a semiconductor material, such as one or more of theabove-noted second generation or later materials, and the plurality ofheterojunction-type discrete contacts may each comprise a buffermaterial and a transparent conducting oxide, and the plurality ofohmic-type discrete contacts may comprise discrete metal contacts to thelight absorption layer. By way of example, the first and second discretecontacts may each be sub-micrometer-sized, for instance, 500 nanometersor less. More particularly, the discrete contacts may have acharacteristic dimension in the range of 100-500 nanometers, and (incertain embodiments) be distributed in spaced rows over the lightabsorption layer. By way of example, the plurality of first discretecontacts and the plurality of second discrete contacts may resideentirely within the passivation layer (i.e., the second surfacepassivation layer), and comprise surfaces that are coplanar with asurface of the passivation layer. For instance, upper surfaces of thefirst and second discrete contacts may be coplanar with an upper surfaceof the passivation layer over which the electrodes are provided.

As a specific example, the first electrode and the second electrode mayinclude interdigitated first and second conductive lines respectivelydisposed over corresponding rows of the pluralities of first and seconddiscrete contacts. Note also that the first and second electrodes maybe, in one or more embodiments, sized to cover or overlie a majority ofthe passivation layer, and thus, overlie a majority of the lightabsorption layer of the photovoltaic cell. For instance, the first andsecond electrodes may cover 90% or more of the passivation and lightabsorption layers. In one implementation, the first and secondelectrodes are formed from a metal layer that overlies all of thepassivation layer and light absorption layer, with the electrodes beingseparated by a thin scribe, which in certain embodiments, may be on theorder of a micron or less, and thus, most all of the passivation andlight absorption layers are covered by the electrodes. As noted, theseelectrodes may advantageously comprise a photon-reflective material,such as silver or aluminum.

To restate, presented herein are photovoltaic cells or solar cells andmanufacturing processes, and particularly, for instance,CIGS/CZTS/organic- or inorganic-Perovskite, etc., thin film photovoltaiccells. The design of the cell is such that the necessary contacts areformed on a common side of the cell's absorber absorption layer.Further, in certain embodiments, the light absorption layer may be fullyenclosed by passivation layers, that is, have passivation layerscovering its opposite first and second surfaces. Light may enter intothe photovoltaic cell through a transparent substrate, and be reflectedby a highly reflecting electrode layer disposed outside the passivatinglayers to reduce cell absorption losses. Interdigitated electrodes, suchas interdigitated back-side electrodes, provide electrical contact tothe solar cell. The back-side electrodes are electrically connected viadiscrete contacts, such as conductive vias, to the absorber layer. Theinterfaces to a p-type absorber layer may be functionalized by n-typedoping and ohmic contacts. The contacts have a pitch of, for instance,100 nm -5000 nm, between adjacent rows of the different types ofdiscrete contacts, and contact openings may be, for instance, 100-500nm, in accordance to the requirements of the lifetime of minority chargecarriers in the cell's light absorption material.

Reference is made below to the drawings, which are not drawn to scalefor ease of understanding, wherein the same reference numbers usedthroughout different figures designate the same or similar components.

FIG. 1 illustrates one embodiment of a photovoltaic cell fabricationprocess 100, in accordance with one or more aspects of the presentinvention. The fabrication process 100 includes providing a transparentsubstrate to allow light to enter the photovoltaic cell 110, andproviding a light absorption layer, such as a thin film semiconductormaterials, in association with the transparent substrate 120. Note inthis regard, that although describing fabricating a photovoltaic cell,those skilled in the art will understand that the process discussed maybe employed to manufacture in parallel a plurality of photovoltaic cellsfor, for instance, a solar panel or other solar device.

The fabricating further includes disposing a passivation layer over thelight absorption layer 130, and providing separate pluralities of firstand second discrete contacts within the passivation layer to facilitateelectrical connection to the light absorption layer 140. First andsecond electrodes are then disposed over the passivation layer and thefirst and second discrete contacts 150. The first and second electrodesmay cover a majority of the photovoltaic cell and be fabricated of aconductive material that is photon-reflective to further enhance cellperformance.

FIGS. 2A-2I depict one detailed embodiment of the above-noted processfor fabricating a photovoltaic cell, in accordance with one or moreaspects of the present invention.

Referring to FIG. 2A, a substrate 200 is provided that is, at least inpart, transparent to allow light to enter the photovoltaic cell throughsubstrate 200. As examples, substrate 200 may comprise a glasssubstrate, a transparent foil substrate, etc.

FIG. 2B depicts the structure of FIG. 2A, after provision of a firstsurface passivation layer 210 and a light absorption layer 220 oversubstrate 200. As shown, light absorption layer 220 includes oppositefirst and second surfaces 221, 222, and first surface passivation layershown disposed over (or covering) first surface 221 of light absorptionlayer 220, between light absorption layer 220 and substrate 200. Notethat in alternate configurations, multiple passivating layers may beprovided between light absorption layer 220 and substrate 200, or nolayers may be provided, in which case light absorption layer 220 mayreside directly on substrate 200.

By way of example, first surface passivation layer 210 may be depositedover substrate 200 using, for instance, atomic layer deposition,sputtering, etc. Exemplary materials for passivation layer 210 includeAl₂O₃, MgF₂, etc. Light absorption layer 220 may be formed of asemiconductor material which is light-absorbing. By way of example, thelight-absorbing material could comprisecopper-indium-gallium-selenide/sulfide (CIGS), copper-zinc-tin-sulfide(CZTS), organic- or inorganic-Perovskite, etc., and be deposited using,for instance, co-evaporation or sputtering processes.

A second surface passivation layer 230 may be deposited over the secondsurface 222 of light absorption layer 220, as illustrated in FIG. 2C. Inone or more implementations, second surface passivation layer 230 may bean antireflective and passivating layer, and may comprise, for instance,Al₂O₃, MgF₂, or other passivating material(s). Note that thicknesses ofthe layers in the stack of FIG. 2C may be provided, as desired. By wayof example, substrate 200 may have a thickness of 100-200 microns. Firstsurface passivation layer 210 may have a thickness in the range of 5-15nanometers, light absorption layer 220 may have a thickness less than 5microns, for instance, in the range of 0.5-2 microns, and second surfacepassivation layer 230 may have a thickness in the range of 5-15nanometers. Note that the thicknesses of the passivation layers 210, 230may be the same, or different, as may be the material forming thepassivating layers.

As illustrated in FIG. 2D, second surface passivation layer 230 ispatterned with a plurality of first contact openings 231 extendingthrough second surface passivation layer 230, to light absorption layer220. The plurality of first contact openings 231 may be formed bydepositing a first sacrificial layer (not shown), such as a polymer,over second surface passivation layer 230, nano-printing openings in thefirst sacrificial layer for the plurality of first contact openings, andthen etching second surface passivation layer 230 to provide theplurality of first contact openings 231 in the desired contact size andpattern. As noted, the resultant discrete contacts being formed are, inone or more embodiments, each sub-micrometer-sized, for instance, 500nanometers or less. Thus, the first contact openings 231 are each formedwith a desired characteristic dimension. For instance, ifcircular-shaped, the first contact openings may have a diameter in therange of 100-500 nanometers, in certain implementations.

As illustrated in FIG. 2E, a thin layer of buffer material 232 may bedeposited within the first contact openings 231, after which the firstsacrificial layer (not shown) may optionally be removed. By way ofexample, buffer material 232 may comprise CdS.

As shown in FIG. 2F, a plurality of heterojunction-type discretecontacts 234 may be formed by depositing, for instance, a transparent,conducting oxide, such as ZnO 233, within the first contact openings 231(FIG. 2E) over buffer material 232. Note that many combinations ofmaterials may be utilized in providing the first discrete contacts 234within second surface passivation layer 230, with the noted materialcombination being provided by way of example only. For instance,alternatively, cadmium-free sputtered ZnOS may be employed in formingthe plurality of heterojunction-type contacts. If not already removed,then after forming first discrete contacts 234, the first sacrificiallayer (not shown) may be removed. Note that alternatively, cadmium-freesputtered ZnOS may be employed in forming the plurality ofheterojunction contacts.

A second sacrificial layer (not shown) may subsequently be provided oversecond surface passivation layer 230 and first discrete contacts 234,and nano-printed for forming second contact openings 235 for theplurality of second discrete contacts. Specifically, after nano-printingthe second sacrificial layer (not shown), the plurality of seconddiscrete contact openings 235 may be formed by etching second surfacepassivation layer 230 using the patterned second sacrificial layer. Aswith the first contact openings, the second contact openings areprovided in the desired contact size and pattern. By way of example, thesecond contact openings 235 may each have a characteristic dimensionless than 500 nanometers, for instance, in the 100-500 nanometer range.

As illustrated in FIG. 2H, a plurality of second discrete contacts 236are formed within the second contact openings 235 (FIG. 2G) bydepositing a desired contact material. In one or more implementations,the second discrete contacts 236 comprise a plurality of ohmic-typediscrete contacts to light absorption layer 220. These contacts may beformed by depositing and planarizing an appropriate back-side contactmaterial or materials, such as Mo, ZnO, ZnO:Al, etc., within the secondcontact openings, after which a metal contact layer 240 is depositedcovering the cell stack. Metal contact layer 240 may comprise aconductive and photon-reflective material, such as, for instance, silveror aluminum.

After forming back-side contact layer 240, a third sacrificial layer(not shown) may be provided over back-side contact layer 240, andnano-printed with openings to etch back-side contact layer 240 to formseparate, interdigitated electrodes 250, 251, as illustrated in FIG. 2I.In one or more implementations, electrodes 250, 251 cover the majorityof second surface passivation layer 230, and thus, the light absorptionlayer 220. As illustrated in FIG. 3, the electrodes may be patterned inany desired (interdigitated) configuration, and may cover, for instance,a majority, such as 95% or more of the cell.

In the embodiment of FIG. 3, electrodes 250, 251 include respectiveconductive lines 252, 253, which are interleaved, by way of example.Note that the conductive lines 252 of first electrode 250 overlie, forinstance, the plurality of first discrete contacts 234, and conductivelines 253 of second electrode 251 overlie the plurality of seconddiscrete contacts 236. After etching to interdigitate the electrodes(such as shown, for instance, in FIG. 3), interconnection betweenphotovoltaic cell electrodes to form the desired photovoltaic device,module, panel, etc., may be made, and conventional packaging orenclosure may be used to complete the photovoltaic device.

Note that numerous variations on the process steps described above inconnection with FIGS. 2A-3 may be employed. For instance, a dielectriclayer could be added onto the second surface passivation layer tofurther improve internal reflection of the light absorption material. Inaddition, for organic-or inorganic-Perovskite, the second surfacepassivation layer (or buffer layer) may be replaced by a hole selectivecontact layer, and the discrete contacts may include nano-sized TiO₂contacts, such as nanowires.

Advantageously, thin film photovoltaic cells are provided herein withboth contact types on one side of the light absorption layer, allowingseparate optimization of the optical design and electrical design, andremoving the requirement for a transparent conducting oxide (TCO) layer,while allowing for improved passivation of the light absorption materialsurfaces, and allowing simplified electrical interconnection ofphotovoltaic cells. In accordance with the designs described herein,small, discrete contacts, such as point- or nano-sized contacts (orvias) are provided within a common passivation layer to, for instance,provide ohmic as well as rectifying contacts to the light absorptionmaterial. In other embodiments, the contacts may becharge-carrier-selective contacts. The thin film photovoltaic or solarcells described may be beneficially employed for CIGS, CZTS, organic- orinorganic-Perovskite, etc., solar cells. The design of the solar cell issuch that the necessary ohmic contacts and heterojunction contacts areformed on one side of the absorber material only. The absorber layer maybe enclosed with passivation layers, and light enters into the cellthrough a light transparent substrate, and is reflected by ahighly-reflecting layer outside the passivation layers, such as thefirst and second electrodes, to further reduce absorption losses. Theback-side contacts advantageously substantially cover the cell andprovide electrical contact to the solar cell. The back-side electrodesare electrically connected iva the discrete contacts, rows of discretecontacts, lines of contacts, etc., to the light absorption layer. Theinterfaces to the light absorption material (e.g., p-type material) arefunctionalized via n-type doping and the ohmic contacts. The contactsmay have a pitch of 100 nm-5000 nm, and the contacts may have acharacteristic dimension in the range of 100-500 nm, in accordance withthe requirements of the lifetime of minority charge carriers and theabsorption material.

As noted, the back-side-only photovoltaic cells and manufacturingmethods disclosed herein address numerous goals, including, forinstance, reducing the thickness of the thin film light absorption layer(i.e., the thin film solar absorber), reducing surface recombination,and increasing photovoltaic cell efficiency. In conventionalphotovoltaic cells, thinning down of the absorber material is preventeddue to the increased absorption and/or recombination at the back contactlayer. In a typical photovoltaic cell with a 2-3 μm thick absorberhaving a typical absorption coefficient, most of the radiation isabsorbed while traveling through the material. The red part of thespectrum is able to travel further through the absorber, and is able toget absorbed/reflected in or at the back contact layer (e.g., Mo layer),increasing the chances for carrier losses. As explained herein, sincethe back contact (e.g., Mo) area is significantly reduced, in accordancewith one or more aspects of the present invention, and sincerecombination is reduced by the presence of the passivation layer, theprior art restriction is overcome. It is less likely that photons willbe absorbed and reflected back by a back-side electrode (e.g., Agelectrode), which is a better mirror than an Mo layer. Hence, theabsorber thickness can be reduced, while maintaining current generationwithin the cell, at the same time as keeping high-voltage levels.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of one or more aspects of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand one or more aspects of the invention for various embodimentswith various modifications as are suited to the particular usecontemplated.

1. A photovoltaic cell comprising: a substrate, the substrate being, atleast in part, transparent to allow light to enter the photovoltaic cellthrough the substrate; a light absorption layer associated with thesubstrate, the light absorption layer having opposite first and secondsurfaces, the first surface being closer to the substrate than thesecond surface; a passivation layer disposed over the second surface ofthe light absorption layer; a plurality of first discrete contacts and aplurality of second discrete contacts, the plurality of first discretecontacts and the plurality of second discrete contacts both residing, atleast in part, within the passivation layer, and facilitating electricalcoupling to the light absorption layer; and a first electrode and asecond electrode disposed over the passivation layer and comprising aphoton reflective material, the first electrode contacting the pluralityof first discrete contacts and the second electrode contacting theplurality of second discrete contacts.
 2. The photovoltaic cell of claim1, wherein the light absorption layer comprises a thin filmsemiconductor material, the thin film semiconductor material having athickness of 5 microns or less, and comprising one ofcopper-indium-gallium-selenide (CIGS), copper-zinc-tin-sulfide (CZTS),or a Perovskite material.
 3. The photovoltaic cell of claim 2, whereinthe plurality of first discrete contacts comprise a plurality ofheterojunction-type discrete contacts to the light absorption layerextending through the passivation layer, and the plurality of seconddiscrete contacts comprise a plurality of ohmic-type contacts to thelight absorption layer extending through the passivation layer.
 4. Thephotovoltaic cell of claim 1, wherein the passivation layer is a secondsurface passivation layer, and wherein the photovoltaic cell furthercomprises a first surface passivation layer disposed over the firstsurface of the light absorption layer, between the substrate and thelight absorption layer.
 5. The photovoltaic cell of claim 4, wherein thefirst surface passivation layer and second surface passivation layercomprise a common passivation material.
 6. The photovoltaic cell ofclaim 1, wherein the plurality of first discrete contacts and theplurality of second discrete contacts extend through the passivationlayer and comprise surfaces co-planar with a surface of the passivationlayer.
 7. The photovoltaic cell of claim 1, wherein the plurality offirst discrete contacts comprise a plurality of heterojunction-typediscrete contacts to the light absorption layer, and the plurality ofsecond discrete contacts comprise a plurality of ohmic-type discretecontacts to the light absorption layer.
 8. The photovoltaic cell ofclaim 7, wherein the light absorption layer comprises a semiconductormaterial, the semiconductor material comprising one ofcopper-indium-gallium-selenide (CIGS), copper-zinc-tin-sulfide (CZTS),or a Perovskite material, and wherein the plurality ofheterojunction-type discrete contacts each comprise a buffer materialand a transparent conducting oxide, and the plurality of ohmic-typediscrete contacts comprise a metal contact to the light absorptionlayer.
 9. The photovoltaic cell of claim 1, wherein the first electrodeand second electrode comprise interdigitated first and second conductivelines, respectively disposed over the corresponding plurality of firstdiscrete contacts and the corresponding plurality of second discretecontacts.
 10. A photovoltaic device comprising: a photovoltaic cell, thephotovoltaic cell comprising: a substrate, the substrate being, at leastin part, transparent to allow light to enter the photovoltaic cellthrough the substrate; a light absorption layer associated with thesubstrate, the light absorption layer having opposite first and secondsurfaces, the first surface being closer to the substrate than thesecond surface; a first surface passivation layer and a second surfacepassivation layer, the first surface passivation layer being disposedover the first surface of the light absorption layer, between thesubstrate and the light absorption layer, and the second surfacepassivation layer being disposed over the second surface of the lightabsorption layer; a plurality of first discrete contacts and a pluralityof second discrete contacts, the plurality of first discrete contactsand the plurality of second discrete contacts both residing, at least inpart, within the second surface passivation layer, and facilitatingelectrical coupling to the light absorption layer; and a first electrodeand a second electrode disposed over the second surface passivationlayer and comprising a photon-reflective material, the first electrodecontacting the plurality of first discrete contacts, and the secondelectrode contacting the plurality of second discrete contacts.
 11. Thephotovoltaic device of claim 10, wherein first discrete contacts of theplurality of first discrete contacts, and second discrete contacts ofthe plurality of second discrete contacts each have a characteristicdimension of 500 nanometers or less.
 12. The photovoltaic device ofclaim 10, wherein the plurality of first discrete contacts are aplurality of first contact vias extending through the second surfacepassivation layer, and the plurality of second discrete contacts are aplurality of second contact vias extending through the second surfacepassivation layer.
 13. The photovoltaic device of claim 10, wherein theplurality of first discrete contacts and the plurality of seconddiscrete contacts extend through the second surface passivation layerand comprise surfaces coplanar with a surface of the second surfacepassivation layer.
 14. The photovoltaic device of claim 10, wherein theplurality of first discrete contacts comprise a plurality ofheterojunction-type discrete contacts to the light absorption layer, andthe plurality of second discrete contacts comprise a plurality ofohmic-type discrete contacts to the light absorption layer.
 15. Thephotovoltaic device of claim 10, wherein the first electrode and thesecond electrode cover at least 90% of the second surface passivationlayer and comprise interdigitated first and second conductive lines,respectively disposed over the corresponding plurality of first discretecontacts and the corresponding plurality of second discrete contacts.16-20. (canceled)